MS Thesis Presentation by Creed Taylor
Wednesday, November 10, 2004

(Dr. Sam V. Shelton, Chair)

"Experimental Measurement of Finned-Tube Heat Exchanger Performance"

Abstract

Finned-tube heat exchangers are predominantly used in space conditioning systems, as well as other applications requiring heat exchange between liquid and gas fluids. One important widespread use is in residential air conditioning systems. These residential cooling systems dictate the peak demand on the U.S. national electrical system, which occurs on the hot summer afternoons, and thereby sets the requirement for the expensive infrastructure requirement of the nation’s power plant and electrical distribution system. In addition to this peak demand, these residential air conditioners are major energy users that dominate residential electrical costs and environmental impact.

The design of finned-tube condenser coils, (heat exchangers), requires the selection of over a dozen design parameters by the designer. The refrigerant side flow and heat transfer characteristics inside the tubes depend mostly on the tube diameter design parameter and have been thoroughly studied. However, the air side flow around the tube bundle and through the fin gaps is much more complex and depends on over a dozen design parameters. Therefore, experimental measurement of the air side performance is needed. Because of the complex nature of the flow and the number of possible heat exchanger designs the air side performance has not been addressed in a comprehensive manner.

First this study built an experimental system and developed methodology for measuring the air side heat transfer and pressure drop characteristics of fin tube heat exchangers. This capability was then used to continue the goal of expanding and clarifying the present knowledge and understanding of air side performance and to enable the air conditioner system designer to verify an optimum fin tube condenser design.

In this study eight finned-tube heat exchangers were tested over an air flow face velocity range of 5 – 12 ft/s. The raw data was reduced to the desired heat transfer and friction data, j and f factors. This reduced heat transfer and friction data was plotted versus Reynolds number and compared. The effect of fin spacing, the number of rows and fin enhancement were all investigated. The heat transfer and friction data were also plotted and compared with various correlations available from open literature. The overall accuracy of each correlation to predict experimental data was investigated.